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Energy Efficient Replacement Windows

Krypton or Argon-Filled, Low-E, Double-Hung Energy Star Units

Windows aren’t what they used to be. Plenty of contractor-grade windows are installed by residential building contractors, but an upgrade to a krypton or argon-filled, low-e, double-hung model will quickly pay for itself.

A residential energy audit will quickly point out which windows will benefit most from replacement.

Why Krypton or Argon-Filled Windows?

Argon is in fact a very useful gas. It’s used inside incandescent light bulbs to keep oxygen from degrading the tungsten filament. It’s used in processing the silicon to make the semiconductors that make reading this article possible.

With the advent of double-paned windows, manufacturers originally flushed the cavity with nitrogen or simply filled it with air. But they quickly discovered that a slower-moving gas reduces conduction, thus minimizing the transfer of heat and cold from the inside to the outside of the dwelling.

Both krypton and Argon fit the bill. Both are non-toxic which places them in the green building arena. Krypton is the more efficient of the two gases, but more expensive, so it is used in cases where the cavity space between the double panes needs to be reduced.

Low-Emittance (Low-E) Coatings as a Radiant Barrier

Low-e coatings are metal or metallic oxide layers that are microscopically thin and almost invisible to the naked eye. The manufacturer applies them to window and skylight glazings. The end result is a reduction of the U-factor by quelling radiant heat flow.

In this respect, low-e coatings, combined with a gas-filled void, function in a manner similar to radiant barrier foil or paint used in conjunction with attic insulation.

There are two categories of coatings which should be taken into account when selecting energy-efficient windows. High solar gain glazing is more effective in winter, but low solar gain (also called sputtered) wins the prize during the summer.

The home’s dominant weather pattern should determine which type will result in lower utility bills.

The Role of Window Frame Material

Many homeowners focus exclusively on the window and its thermal properties. But consider that the frame itself comprises anywhere from 10 to 30 percent of the unit’s surface area. It’s no surprise that the material has an impact on efficiency.

• Aluminum: This material is extruded so it’s a good choice for complex arcs and other shapes. A disadvantage is high thermal conductance. It’s also notorious for condensation and even frost inside the home in very cold weather.

• Aluminum with a Thermal Break: In an attempt to reduce thermal conductance, the inside of the frame is separated from the outside and a less conductive material is place between the two sides.

• Vinyl: Actually this is polyvinyl chloride, or the familiar PVC used in residential plumbing applications. It provides a good insulating factor and the color is permanent since it goes all the way through; there’s no need to paint.

• Insulated Vinyl: This is the same as regular vinyl with an insulated core designed to improve thermal performance.

• Fiberglass: This material is also known in the industry as glass fiber reinforced polyester. It’s extruded like aluminum, but offers superior thermal qualities.

• Wood Window Frames: Wood is the most traditional of all frames. Since it needs to be painted, changing the home’s color scheme is a snap. It can also be fashioned into complex shapes. Routine maintenance is important since wood is susceptible to rotting.